The present invention relates to an improved process for the production of copolyesters. More particularly, it relates to a process for the production of oxybenzoyl polyesters of aromatic dicarboxylic acids, dihydroxyphenols and p-hydroxybenzoic acid compounds as the starting materials.
It is known that such polyester resins can be produced by various polymerization processes including suspension polymerization and bulk polymerization. Of these, the bulk polymerization process is perhaps the most desirable process in terms of economy. However, since the aromatic polyesters have a high melting point as compared with aliphatic polyesters, such as polyethylene terephthalate, a higher temperature is required to maintain the aromatic polyesters at their molten state. Consequently, the polymers are often colored and deteriorated in performance.
Further, difficulty has been experienced in obtaining lot-to-lot consistency in molding characteristics of the resin. Obviously, variations in molding conditions are undesirable in commercial operations and can result in inefficiencies of operation and unacceptable differences in the molded articles.
Much effort has therefore been expended on the development of a process which eliminates the disadvantages discussed above and provides a polyester molding material from which articles of pleasing and uniform appearance and properties can be obtained.